"We also want to acknowledge that there are going to be some things that developers want to do that just aren't supported by the platform. Rather than granting additional privileges to accommodate those requests, we encourage developers to focus on what's possible within the rich variety of integration options already provided."

I can't tell you for sure what that means, but I can tell you what I think it means. Twitter makes the back-end system and they make apps. They are going to make features available to their apps that are not available to competitive apps. Presumably features that users will want and/or will make Twitter money.

Microsoft did something like that, connecting their operating system -- Windows -- and their apps: Excel, Word, Powerpoint, et al. There were private APIs that made their apps run better than 1-2-3, WordPerfect, etc. Microsoft denied they were doing it.

Twitter is not only are they admitting they're doing it, but they're giving developers a heads-up. They may regret doing that, because the developers aren't entirely without options. They also might regret doing it because they are sheltering internal developers from competition, and developers without competition are lazy developers. Hard to motivate.